Bodies in Motion is an ongoing photographic project that aims to document the power, beauty and possibility of the human body in motion. It is freely accessible to all visitors at preview resolution or you can subscribe for higher quality images.
Frame by Frame is a blog that displays sequential images from various animated films for study and appreciation. It also shows the gif to supply reference for timing.
The Smearframe Slack channel is an animation chat group where you can talk about anything from inspiration, tips, rigs and more. Get an invite from the link above and join the fun!
The Fighters Generation is a world renowned character database… featuring just about every fighting game character in existence. It boasts an unparalleled collection of the best quality artwork, pictures & animations!
Kenny Roy is a 16 year veteran of the animation industry, and 7 year Mentor from Animation Mentor. Sign up to his members section for Monthly Videos, In-Depth Articles and more!
Newgrounds is a popular website for posting animations, games and audio and has been around for over 20 years. Founded by Tom Fulp (also founder of The Behemoth [game developer])
Brendan Body has a great post on his website which displays lots of great reference and observations on birds and flight.
Animators Resource is a similar website to this one but focuses more on specific posts and videos rather than linking to other websites.
Animator's Resource Kit 